The present invention relates to a method of producing bisphenol A [2,2-bis(4-hydroxyphenyl) propane]. More specifically, the present invention relates to an industrially useful method of producing bisphenol A in which, in the production of bisphenol A from phenol and acetone with the use of a cation exchange resin as a catalyst and a free mercaptan as a promoter, a multi-stage reactor is employed, whereby elimination of sulfonic groups from the cation exchange resin can be suppressed, so that bisphenol A of high quality can be obtained, and the amount of the catalyst used can be reduced.
Bisphenol A has been known as an important compound for raw material for engineering plastics, such as polycarbonate resins, polyacrylate resins, etc, or for epoxy resins, and the demand for it tends to be still more growing recently.
Bisphenol A is produced by the condensation of an excess of phenol and acetone in the presence of an acid catalyst and optionally a promoter, such as a sulfur compound, etc.
As the acid catalyst for that reaction, inorganic mineral acids, such as sulfuric acid, hydrochloric acid, etc. were conventionally used. However, cation exchange resins have recently attracted attention (GB Patent Nos. 842209, 849565 and 883391), and have come to be industrially used.
On the other hand, it has been known that as for sulfur compounds used as the promoter, alkyl mercaptans with or without substituting groups, such as methyl mercaptan, ethyl mercaptan, thioglycolic acid, etc., are useful (U.S. Pat. Nos. 2,359,242 and 2,775,620). The mercaptans function to increase the reaction rate and improve the selectivity. For example, as reaction by-products in the production of bisphenol A, 2-(2-hydroxyphenyl)-2-(4-hydroxyphenyl) propane (a combination of o and pxe2x80x2-types) is mainly formed, and tris-phenol, polyphenol, etc. are also formed. Especially, in cases where bisphenol A is used as raw material for polycarbonate resins, polyacrylate resins, etc., required is colorless high purity bisphenol A containing a reduced amount of those by-products. To this end, mercaptans are used as a promoter in order not only to increase the reaction rate but also to suppress the formation of the by-products and increase the selectivity.
With respect to the reaction temperature at which phenol and acetone are condensed to produce bisphenol A, disclosed are, for example, (1) the method in which phenol and acetone are subjected to a catalytic reaction with the addition of ethyl mercaptan at a reaction temperature of 60-85xc2x0 C. (Japanese Patent Publication No. 52(1977)-12700), (2) the method in which phenol and acetone are reacted at a molar ratio of phenol/acetone of 2-10 in the presence of a strong acid at a temperature not exceeding 80xc2x0 C. (Japanese Patent Publication No. 52(1977)-42790), (3) the method in which acetone is substantially completely reacted in the presence of an acidic chemical agent at a temperature not exceeding 80xc2x0 C. (Japanese Patent Publication No. 57(1982)-14329).
However, in the above method (1), there is a prerequisite in that the reaction is carried out in one step, and it is required that the degree of conversion be made low or the temperature at the inlet be made low and the amount of the catalyst be made large when a adiabatic reactor with a fixed bed is used under such prerequisite at temperatures not greater than 85xc2x0 C. Thus, the above method (1) is not efficient. On the other hand, in both the above methods (2) and (3), there is a prerequisite in that hydrochloric acid or sulfuric acid is used as the catalyst, and cation exchange resins are not used.